X-ray device



ZA-QQMQ Dec. 6, 1949 I J. M. LEDEBOER X-RAY DEVICE Filed April 16, 1946unlnlnlvo Illl'llll lllllllllil'llllll.

n-uuininna noun JOE 1N MARIE LEDEB OER.

I N VEN TOR.

Patented Dec. 6, 1949 X-RAY DEVICE Johan Marie Ledeboer, Eindhoven,Netherlands, assignor, by mesne assignments, to Hartford National Bankand Trust Company, Hartford,

Conn, as trustee Application April 16, 1946, Serial No. 662,427 In theNetherlands November 17, 1943 Section 1, Public Law 690, August 8, 1946Patent expires November 17, 1963 3 Claims.

X-ray devices are known in which the devices regulating the voltage andthe loading period are coupled with a device for regulating the currentstrength in such a manner that this current is adjusted to a lower valueas the voltage chosen is higher or the chosen loading period is longer.

To this end the heatin circuit may comprise two series-connectedresistances one of which comprises a regulating member which is coupledwith the voltage selector, whereas the other comprises a regulatingmember coupled with the time selector. The control stages of the firstresistance are chosen in such a manner that in a definite position ofthe time selector (i. e. of the second regulating member) the powersupplied to the X-r-ay tube is the same in all positions of the voltageselector and has more particularly such a value that the X-ray tube isjust capable of withstanding during the loading period which is adjustedby means of the time selector. Consequently, as long as the timeadjustment is not changed, the current strength is inverselyproportion-a1 to the voltage which is adjusted .by means of the voltageselector.

The control stages of the second resistance are chosen in such a mannerthat even in any arbitrary position of the time selector the power(which in this case must have a different value in any instance) hassuch a value that the X-ray tube is just capable of withstanding duringthe loading period then adjusted. To permit this use is made of a seriesresistance Whose value has been adjusted permanently and is leftunchanged while the voltage and the time are regulated during normaloperation of the X-ray apparatus. Experimentally and by readjustment ofthe three resistances the operator finds a division in which the imposedcondition is satisfied, with a sufficient degree of approximation inpractice, for all positions of the selectors.

When replacing the X-ray tube, for instance in the case of a failure,the three resistances must be controlled, since the spare tube mayexhibit such differences, in regard to the functional relation existingbetween anode-current strength and filament current strength, thatwithout readjust ment of the resistances it would no longer receive thedesired load in every position of the selectors. Sometimes a slightmodification or the seriesresistance is suflicient, but it also occursthat the resistances coupled with the selectors must be adjusted anew.This is to be considered as a drawback of this device, notably in thecase of regulators with continuous control.

This drawback is much more manifest when tubes of a difierent kind areto be connected alternately to one and the same apparatus. In this caseother tappings from th resistances of the filament circuit must be usedfor each tube, which requires an intricate changing over mechanism.Moreover, each series of tappings must be readjustable in view ofreplacement, if required.

This disadvantage is overcome b the present invention which has for itsobject to approximate with a sufiicient degree of accurac (which maystill be raised by another improvement according to the invention) themaximum permissible current strength at each adjustable value of thevoltage and the loading period and with every X-ray tube by means of asmall number of resistance tappings.

The invention is directed to an X-ray apparatus comprising a regulatingdevice for the tube current, which is coupled with the voltage selector,and another regulating device for the tube current, which is coupledwith the time selector. According to the invention the tube current iscontrolled by means of resistances inserted, through the intermediary oftransformers having a variable transformation ratio, in the cathodeheating circuit of the Xray tube. Consequently, the resistance stagesare all varied to the same degree upon modification of thetransformation ratio. We have found that this permits the retention ofthe result once obtained upon replacement of the X-ray tube. In a deviceaccording to the invention solely a difierent transformation ratio and,as the case may be, a different value of the series resistance must bechosen to match all resistance stages simultaneously to the load of thenew tube according to its nomogram. Consequently, it is sufficient toprovide a readjustable tap solel for the transformers and the seriesresistance. It is advantageous to provide it with the transformers bothon the primary and on the secondary side, since in this case less connecting points are required than in the case of readjustability at onlyone of the windings.

Even when different X-ray tubes are to be connected alternately to theapparatus the property round may be utilized to make the interchangingof tappings of the regulating resistances superfluous and thus avoidintricate switching mechanisms. To this end, with the transformer towhich the regulating resistances are connected and the series resistancea separate tapping is provided for every tube, which tap ing may, in itsturn, be readjustable in View of possible replacement of the tubes.Devices for changing over these tappings, consequently for modifying thetransformation ratio of the transformers, may be coupled electrically ormechanically with the device for selecting the tube, so that on changingover the tubes the vtappings from the control transformers associatedwith the tube chosen are put into use simultaneously.

In practice it is mostly desirable that the voltage selector should havea linear scale division and .the time selector should have a logarithmicscale division. Often this condition can be satisfied only by anon-linear division of the current regulating resistances. In this casethe division can be made linear again by varying the resistance per unitlength of the wire or band constituting the resistance to be regulated.This is of particular importance for continuous regulators.

When in an apparatus comprising more than one tube the division of theresistance, upon changing over from one tube to the other, is to bemodified, this method is unsuitable. In the apparatus according to theinvention it may also be utilized when using two-or more tubes, sinceinthis case the resistancezstages steadily retain the same value. Thisconstitutes another advantage of the invention.

The series resistance and the control stages of the resistances coupledwith the selectors may, it is true, be chosen in such a manner that inno position of the selectors the power exceeds that which theX-ray tubeis capable of withstanding at themost during the loading period chosenand the deviations from the optimum loading state always remain withinreasonable limits, but a perfectly correct adjustment of the power withany desirable combination of voltage and time cannot be ensured withoutchanging over of the connections of the regulating resistances. Even ifone of the regulating resistances is replaced by a voltage regulator, sothat the influence of the summing of the resistances is cancelled,deviations from the ideal. loading state remain. One of the causesthereof is, for instance, th variation of thevoltage loss in theapparatus in the case of a varying current strength. Wrongadjustmentsare also caused by the fact that the anode current of the X-ray tube,even within the control range, is not proportional to thefilamentcurrent- In the case of a greater accuracyof adjustment being requiredcertain corrections are necessary in regard to the tappings from theregulating resistances. In a=device according to the invention thesecorrections are possible in a simple manner. In fact, we have found thatin the case of a suitable division of the total resistance in thecathode heating circuit over the series resistance and the tworegulating resistances, the required corrections of the. resistancevariations necessary for the obtainment of the optimum loading states,which variations the regulating resistance coupled with one of the twoselectors must undergo successively on traversing all positions of theother selector, approximately have the same ratio for all positions ofthe first-mentioned selector.

Consequently, according to the invention, on passing overfrom .oneposition of one selector to another position of the same selector, allresistance stages of the-current regulator coupled with the otherselector can be .corrected simultaneously, by giving the transformer, towhich this current regulator is connected, a different transformationratio. This .does not require special care during operation, if thevoltage selector has coupled to it itsOWn" current regulator and inaddition (electrically or mechanically) a member for varying thetransformation ratio of the transformer, to which is connected thecurrent regulator coupled with the current selector, and conversely thetime selector has coupled to it a member for modifying thetransformation ratio of the transformer having connected to it thecurrent regulator coupled with the voltage selectcr.

In this construction the total number of tappings of the transformersand resistances required for steadily obtaining the maximum permissibleload does not exceed twice the sum of the number of positions of the twoselectors viz. once from the resistances and once from the transformers.However, the number of tappings from the transformers may be materiallyreduced without any appreciable decrease in accuracy. The series ofresistance values corresponding with the control stages of one of theselectors, which is required in a definite position of the otherselector, is but slightly different from that re.- quired in aneighbouring position of the lastmentioned selector. This permits thechanging over of the transformers to take place in any instance aftertraversing a certain number of stages of voltage or time and.consequently to simplify the construction of the X-ray device. In thiscase a few correction tappings are sulficient.

In order that the invention may be clearly understood and readilycarried into effect, it will now be described more. fully with referenceto the accompanying drawing, representing, by way of example a wiringdiagram of an X-ray apparatus according to the invention, to which threeX-ray tubes 2 and 3 can be connected. The supply transformer isconnected on its primary side to a regulating transformer 5 which,through the intermediary of an auto-transformer 6 having a variablenumber of primary turns, is connected to the mains terminals.

The cathode heating current for the X-ray tubes is supplied by thetransformer 1 to which a stabilized voltage is fed. The primary circuitof this transformer comprises two regulating devices 8 and 9 and a.seriesresistance I0. The regulating devices 8 and 9 each comprise aresistance (I l and I2) and a transformer (l3 and Hi). Two switches 23and 24 correspond with readjustable tappings of the secondary windingsof the transformers. By operating these switches or shifting thetappings themselves the trans formation ratio of these transformers ischanged. Tothe secondary windings are connected the resistances llandlZv which are provided with a certain number-of tappings over whichpass contact arms 25 and 26. The members 23 and 26 are electrically ormechanically coupled with the contact arm of the voltage regulator 5 andthe members 24 and 25 are electrically or mechanically coupled'witharegulator 21 by means of which the loading period is adjusted- Theprimary windings of the transformers I3 and it also comprise a certainnumber of readjustable tappings which permit the transformation ratio tobe modified. In the executional example are indicated three tappings'inaccordance with the number'of tubes which must be fed alternatelyby-means of thedevice. The contact arms l5 and I6, which establish theconnection between one of the supply conductors and the transformertappings are coupled, either mechanically or electrically, with the tubeselec tor I I also having. three positions. The tube selector operatesat the same time as the switching arms I8, i9, 28 and ZI thusestablishing all connections required for operating a definite tube.

Moreover, the switching arms I5 and I6 are coupled with the regulatingmember 22 of the series resistance It. By means of this seriesresistance the total resistance of the filament circuit for every X-raytube is given the value which is most suitable in view of the individualproperties of the tube. The optimum division of the required resistanceover the three elements II], II and I2, can be found experimentally.

When the tappings of the transformers I3 and I4 are chosen correctly,the positions of the regulators 25 and 26 are suitable for every tubeconnected. The tappings are readjustable to permit correction uponreplacement of a tube in order that the regulating devices for the newtube shall operate as accurately as possible.

A displacement of the voltage selector 5 or the time selector 2'Iinvolves a variation of the current regulating resistance I2 and IIrespectively. For several reasons this requires correction of the othercurrent regulating resistance II and I2 respectively, which correctionis brought about automatically by the simultaneous modification of thetransformation ratio of the transformer I3 and I4 respectively by meansof the switch 23 and 24 respectively. However, the necessary correctionis small so that it is sufficient to divide the control stages intogroups and to modify the transformation ratio slightly only on passingover from one group to the other. In the executional example two groupsare chosen, so that two readjustable correction tappings are provided onthe secondary windings of the transformers. The correction tappings mayalso be provided on a separate transformer connected in cascade with thetransformer I3 and I4 respectively. As an alternative they may beprovided at the primary side instead of at the secondary side.

The regulator 28 serves to adjust the feed voltage of the high-tensiontransformer to a definite value, prior to an X-ray exposure, andconsequently for the so-called mains voltage correction.

What I claim is:

1. X-ray apparatus comprising an X-ray tube having anode and cathodeelectrodes, circuit 5 means to energize said cathode electrodecomprising first, second, and third variable resistance elements, firstand second transformers each having an adjustable primary winding tovary the transformation ratio thereof and a secondary winding, meanscoupling the secondaries of said first and second transformers to saidfirst and second resistance elements respectively, means connecting saidprimary windings in series with said cathode and said third resistanceelement, circuit means for energizing said anode electrode including avoltage regulating member and a time adjusting member for adjusting theloading time of said tube, means coupling said voltage regulating memberto the first of said resistance elements to adjust said first resistanceelement in accordance with the adjustment of said voltage adjustingmember, and means coupling said time adjusting member to the second ofsaid resistance elements to adjust said second resistance element inaccordance with the adjustment of the loading time of said tube.

2. X-ray apparatus as claimed in claim 1 for controlling a plurality ofX-ray tubes in which the means for adjusting the primary windings ofsaid transformers are coupled to means for adjusting said thirdresistance element and a selector switch for selecting one of said tubesand connecting said tube to said cathode and anode energizing circuits.

3. X-ray apparatus as claimed in claim 1 in which the secondary windingsof said transformers are adjustable to vary the transformation ratios ofsaid transformers including means coupling the secondary winding of saidfirst transformer to said time adjusting member to adjust the secondarywinding of said first transformer in accordance with the adjustment ofthe loading time of the tube, and means coupling the secondary windingof said second transformer to said voltage adjusting member to adjustthe secondary winding of said second transformer in accordance with theadjustment of the loading time of the tube.

J OHAN MARIE LEDEBOER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,053,587 Van Den Berg Sept. 8,1936 2,250,301 Fathauer July 22, 1941 2,368,798 Ball Feb. 6, 1945

